The present invention provides a novel process for producing 2,6,6-trimethyl-2-cyclohexene-1,4-dione (keto-isophorone) by catalytic oxidation of 3,5,5-trimethylcyclohexa-3-ene-1-one (β-isophorone) with hydrogen peroxide as the oxidant.
The present invention relates to the epoxidation of 3,5,5-trimethylcyclohexa-3-ene-1-one (β-isophorone, β-IP) and the direct further reaction of this compound to afford 2,6,6-trimethyl-2-cyclohexene-1,4-dione (keto-isophorone) using a catalyst system consisting of a tungsten salt (sodium tungstate), phosphoric acid and a phase transfer reagent in a one-pot synthesis.
Isophorone (IP) is obtained by condensation of acetone—it is the trimeric condensation product. After the reaction a mixture of the isomers 3,5,5-trimethylcyclohexa-2-ene-1-one (α-isophorone) and 3,5,5-trimethylcyclohexa-3-ene-1-one (β-isophorone) (U.S. Pat. No. 8,889,914 B2) is present.
Isomerization of 3,5,5-trimethylcyclohexa-2-ene-1-one (α-isophorone) in the liquid phase in the presence of a homogeneous or heterogeneous catalyst (DE 19639569 A1) makes it possible to produce 3,5,5-trimethylcyclohexa-3-ene-1-one (β-isophorone) in very good yields.
Trimethylhydroquinone diacetate (TMHQ-DA), which may be used as a precursor for the production of vitamin E, may be produced starting from β-IP. Thus, IP provides a route to vitamin E and can in this regard be viewed as an alternative to trimethylphenol which is likewise a precursor of vitamin E.
One important and, for existing processes, economy-determining step for the production of vitamin E starting from isophorone (IP) is the conversion into the intermediate keto-isophorone.
The oxidation of β-isophorone using peroxycarboxylic acids to afford epoxy-isophorone is known from the literature (DE 110024265/U.S. Pat. No. 6,469,215). The examples describe not only the oxidation of β-isophorone but also the production of perpropionic acid from propionic acid and hydrogen peroxide and the conversion of epoxy-isophorone into dihydroketo-isophorone.
However, the large number of reaction steps and process steps to arrive at keto-isophorone and the use of safety-critical peroxycarboxylic acids and costly catalyst systems is a great disadvantage of this method on both economic and safety grounds.
The direct oxidation of β-Isophorone to afford keto-isophorone is also known (DE 19619570). Here, the β-isophorone is oxidized with oxygen using a costly manganese-salen catalyst at elevated pressure (up to 10 bar). The elevated pressure and the requirement for using pure oxygen present a safety engineering challenge for the construction of production plants.
The direct oxidation of α-isophorone to afford ketoisophorone directly is also described in scientific publications (1.) Catalysis Commun 11_2010_758-762/2.) Applied Catalysis A General 345_2008_104-111. However, the keto-isophorone conversions and selectivities are too low, and the catalysts and/or oxidants used (for example organic peroxo compounds or N-hydroxyphthalimides (NHPI)) too costly, to produce keto-isophorone on a large industrial scale.